Compositional Effects in the Retention of Colloids by Thermal Field-Flow Fractionation

Jeon, Sun Joo; Schimpf, Martin E.; Nyborg, Andrew C.

doi:10.1021/ac9613040

Cited by 52 publications

(56 citation statements)

References 18 publications

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“…1, molecules characteristically deplete from regions with an increased temperature, but they can also show the inverted effect and accumulate (2,3). Moreover, the size scaling of thermodiffusion recorded by thermal field flow fractionation showed fractional power laws with a variety of exponents that are hard to interpret (4,5). The latter effect might be resolved by revealing nonlinear thermophoretic drift for the strong thermal gradients used in thermal field flow fractionation (our unpublished observations).…”

mentioning

confidence: 87%

Why molecules move along a temperature gradient

Duhr

Braun

2006

Proc. Natl. Acad. Sci. U.S.A.

902

987

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Molecules drift along temperature gradients, an effect called thermophoresis, the Soret effect, or thermodiffusion. In liquids, its theoretical foundation is the subject of a long-standing debate. By using an all-optical microfluidic fluorescence method, we present experimental results for DNA and polystyrene beads over a large range of particle sizes, salt concentrations, and temperatures. The data support a unifying theory based on solvation entropy. Stated in simple terms, the Soret coefficient is given by the negative solvation entropy, divided by kT. The theory predicts the thermodiffusion of polystyrene beads and DNA without any free parameters. We assume a local thermodynamic equilibrium of the solvent molecules around the molecule. This assumption is fulfilled for moderate temperature gradients below a fluctuation criterion. For both DNA and polystyrene beads, thermophoretic motion changes sign at lower temperatures. This thermophilicity toward lower temperatures is attributed to an increasing positive entropy of hydration, whereas the generally dominating thermophobicity is explained by the negative entropy of ionic shielding. The understanding of thermodiffusion sets the stage for detailed probing of solvation properties of colloids and biomolecules. For example, we successfully determine the effective charge of DNA and beads over a size range that is not accessible with electrophoresis.DNA ͉ fluorescence ͉ microfluidic ͉ Soret ͉ thermodiffusion T hermodiffusion has been known for a long time (1), but its theoretical explanation for molecules in liquids is still under debate. The search for a theoretical understanding is motivated by the fact that thermodiffusion in water might lead to powerful all-optical screening methods for biomolecules and colloids. Equally well, thermodiffusion handles and moves molecules alloptically and therefore can complement well established methods: for example, electrophoresis or optical tweezers. For the latter, forces of optical tweezers scale with particle volume and limit this method to particles of only Ͼ500 nm. Electrophoresis does not suffer from force limitations but is difficult to miniaturize because of electrochemical reactions at the electrodes.On the other hand, thermodiffusion allows the microscale manipulation of small particles and molecules. For example, 1,000-bp DNA can be patterned arbitrarily in bulk water (Fig. 1). The temperature pattern ''DNA,'' heated by 2 K, was written into a water film with an infrared laser scanning microscope. The concentration of 1,000-bp DNA was imaged by using a fluorescent DNA tag. In an overall cooled chamber at 3°C, DNA accumulates toward the heated letters ''DNA'' (negative Soret effect), whereas at room temperature DNA is thermophobic (positive Soret effect) as seen by the dark letters.In the past, the apparent complexity of thermodiffusion prevented a full theoretical description. As seen for DNA in Fig. 1, molecules characteristically deplete from regions with an increased temperature, but they can also show the inver...

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mentioning

confidence: 87%

Why molecules move along a temperature gradient

Duhr

Braun

2006

Proc. Natl. Acad. Sci. U.S.A.

902

987

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“…Thermophoresis is theoretically not yet understood. Experimental methods to measure thermophoresis of colloids in aqueous and nonaqueous suspensions are quite diverse and use thermal field flow fractionation (ThFFF) [5,6], beam deflection [2,4,7], holographic scattering [3,8,9], thermal lensing [10], and optical heating in microfluidics [11,12]. Thermophoresis has the potential to analyze the particle-solvent interaction of nanoscaled particles and biomolecules.…”

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confidence: 99%

“…(5) and (6). Locally, temperature and concentration differences are small and a linearized Boltzmann distribution holds:…”

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confidence: 99%

Thermophoretic Depletion Follows Boltzmann Distribution

2006

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Thermophoresis, also termed thermal diffusion or the Soret effect, moves particles along temperature gradients. For particles in liquids, the effect lacks a theoretical explanation. We present experimental results at moderate thermal gradients: (i) Thermophoretic depletion of 200 nm polystyrene spheres in water follows an exponential distribution over 2 orders of magnitude in concentration; (ii) Soret coefficients scale linearly with the sphere's surface area. Based on the experiments, it is argued that local thermodynamic equilibrium is a good starting point to describe thermophoresis.

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“…Despite numerous empirical studies and proposed theories [54][55][56][57][58], thermal diffusion remains an intriguing, but highly useful, aspect of ThFFF separations. Composition-based separations have been demonstrated for both polymers [59][60][61] and particles [62]. This topic is discussed further in a later section.…”

Section: Thfffmentioning

confidence: 94%

Field‐flow fractionation of proteins, polysaccharides, synthetic polymers, and supramolecular assemblies

Williams¹,

Lee

2006

J of Separation Science

125

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This review summarizes developments and applications of flow and thermal field-flow fractionation (FFF) in the areas of macromolecules and supramolecular assemblies. In the past 10 years, the use of these FFF techniques has extended beyond determining diffusion coefficients, hydrodynamic diameters, and molecular weights of standards. Complex samples as diverse as polysaccharides, prion particles, and block copolymers have been characterized and processes such as aggregation, stability, and infectivity have been monitored. The open channel design used in FFF makes it a gentle separation technique for high- and ultrahigh-molecular weight macromolecules, aggregates, and self-assembled complexes. Coupling FFF with other techniques such as multiangle light scattering and MS provides additional invaluable information about conformation, branching, and identity.

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Compositional Effects in the Retention of Colloids by Thermal Field-Flow Fractionation

Cited by 52 publications

References 18 publications

Why molecules move along a temperature gradient

Why molecules move along a temperature gradient

Thermophoretic Depletion Follows Boltzmann Distribution

Field‐flow fractionation of proteins, polysaccharides, synthetic polymers, and supramolecular assemblies

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